1. Field of the Invention
The present invention relates to a fixing device and an image forming apparatus having such a fixing device.
2. Description of the Related Art
Image forming apparatuses such as a printer, a facsimile machine, a photocopier, and a multifunctional peripheral having these functions are generally configured to form images including characters or symbols on recording media such as paper, cloth, and OHP sheets based on image information. In particular, electrophotographic image forming apparatuses are widely used for forming high definition images composed of resin particles on plain paper at high speeds. Note that the resin particles indicate particles containing resin as one of their components. Toner has particles specifically used in the electrophotographic image forming apparatuses. Toner contains materials to generate necessary functions for forming images by the electrophotographic image forming apparatuses, such as a charge control agent to generate an electrostatic property in the resin particles, a coloring material to generate colors, and a material to prevent the particles from binding. In the electrophotographic image forming apparatus, a fixing speed is high and the quality of the fixed image is generally high. Thus, a thermal fixing system is widely used in the electrophotographic image forming apparatus. In the thermal fixing system, toner residing on a recording medium is melted, and pressure is applied to the melted toner on the medium, thereby fixing the toner on the recording medium. However, in the electrophotographic image forming apparatus having the thermal fixing system, more than half of the power is consumed for heating the toner, which makes it difficult to achieve energy savings technology in the electrophotographic image forming apparatus.
In view of recent environmental concerns, the development of a low power consumption (energy-saving) fixing device has been desired. That is, a fixing device having a non-thermal fixing system (hereinafter also called a “non-thermal fixing device”) capable of fixing toner on the recording medium without heating has been desired. An example of such a non-thermal fixing system is disclosed in Japanese Patent Application Publication No. 2007-219105 (hereinafter referred to as “Patent Document 1”). Patent Document 1 discloses a wet fixing system in which a fixer (liquid fixer) is generated in a foam state and the generated foam fixer is applied onto resin particles on a recording medium while controlling a film thickness of the foam fixer, thereby fixing resin particles on the recording medium. Note that there are numerous types of softeners used in this system, an example of which include aliphatic ester disclosed in Japanese Patent Application Publication No. 2008-102300 (hereinafter referred to as “Patent Document 2”). However, non-volatile softeners may be preferable in view of an environmental problem for volatile organic compounds or adverse effect of the softener on the human body. Note that Patent Document 1 also discloses a fixing device in which a fixer containing a softener to soften resin particles by melting or swelling at least part of the resin is applied to the resin particles residing on the recording medium to thereby fix the resin particles on the recording medium. The fixing device disclosed in Patent Document 1 includes a foam fixer generator unit configured to generate a fixer in a foam state, a film thickness control unit configured to control a film thickness of the generated fixer in the foam state, and an application unit configured to apply the generated fixer in the foam state to the resin particles residing on the recording medium. Moreover, Patent Document 2 discloses a fixing method in which are applied a fixer containing a softener to soften resin by melting or swelling at least part of the resin to resin particles and a component for controlling the softening of the resin by allowing the softener to react with the fixer.
However, in the wet fixing method disclosed in Patent Document 1, if a non-volatile softener is used in particular, the softener remains in the toner and the toner thus remains soft after the toner is being fixed on the recording medium. Accordingly, the image formed on the recording medium may have tackiness (i.e., instantaneous tackiness). With this method, if two or more recording media such as paper on which images are correspondingly formed are mutually stacked, an image bleed-through or strike-through may occur, or missing images in the media due to the bleed-through or strike-through may occur.